1. Field of the Invention
The present invention relates to a multi-band Orthogonal Frequency Division Multiplexing (OFDM). More particularly, the present invention relates to an interleaving method that can increase data transmission efficiency.
2. Description of the Related Art
In the Multi-Band Orthogonal Frequency Division Multiplexing (OFDM) Alliance (MBOA), data are transmitted and received by dividing a frequency into a plurality of 528 MHz bands and performing frequency hopping. Data are transmitted in an OFDM modulation method by using one band selected from the multiple 528 MHz bands. An OFDM carrier is generated based on 128-point Fast Fourier Transform (FFT)/Inverse FFT (IFFT).
In comparison with other standards, the current MBOA Standards aim for high-speed data transmission. The Application Specific Integrated Circuit (ASIC) does not usually operate at 528 MHz, but at 132 MHz, which is a fourth of 528 MHz. Thus, the ASIC processes 528 MHz data by performing four parallel operations inside and this calls for the development of a new interleaving scheme suitable for performing the four parallel operations.
Hereinafter, an interleaving method for performing four parallel operations to transmit data at a high rate in an OFDM system will be described. Interleaving is a method where data are transmitted after the position of the data is changed so that data error transmitted from a transmitting end in a receiving end could be corrected efficiently. In other words, when an error occurs in a particular part of transmitted data, the receiving end cannot correct the transmission error. To solve the problem, the transmitting end transmits the data after changing the position of the transmitted data. Then, although errors occur intensively in a particular part of the data, the receiving end does not centralize the errors in the particular part but disperses the errors into various locations by restoring the data to the original positions. Since the errors are scattered into various parts, the receiving end can efficiently correct the errors. In other words, when transmission errors occur in five consecutive bits, the receiving end cannot correct the transmission error in the five consecutive bits. However, if the transmission errors have occurred in five non-consecutive bits, the receiving end can correct the transmission errors efficiently, compared to the case where the transmission errors have occurred in the five consecutive bits.
As shown above, the MBOA performs interleaving to enhance the data transmission efficiency. In connection with the conventional MBOA, a symbol interleaving scheme and a tone interleaving scheme have been suggested. Hereinafter, the symbol interleaving scheme and the tone interleaving scheme will be described. [Table 1] presents transmission data.
TABLE 10123456789. . .2021222324252627282930313233343536373839. . .5051525354555657585960616263646566676869. . .8081828384858687888990919293949596979899. . .110111112113114115116117118119120121122123124125126127128129. . .140141142143144145146147148149150151152153154155156157158159. . .170171172173174175176177178179180181182183184185186187188189. . .200201202203204205206207208209210211212213214215216217218219. . .230231232233234235236237238239240241242243244245246247248249. . .260261262263264265266267268269270271272273274275276277278279. . .290291292293294295296297298299
The following [Table 2] presents a sequence for reading the data registered in the [Table 1] to interleave the data according to the symbol interleaving scheme. Particularly, the [Table 2] shows interleaving based on a modular 3 operation, when the data rate is 53.3 Mbps. Herein, the data are stored in a memory on a basis of 300 bits and the NCBPS symbol is 100 bits, the CBPS signifying Coded bits per OFDM symbol.
TABLE 20369121518212427. . .6063666972757881848790939699102105108111114117. . .150153156159162165168171174177180183186189192195198201204207. . .240243246249252255258261264267270273276279282285288291294297. . .3134374043464952555861646770737679828588. . .121124127130133136139142145148151154157160163166169172175178. . .11214217220223226229232235238241244247250253256259262265268. . .2581114172023262932353841444750535659. . .929598101104107110113116119122125128131134137140143146149. . .182185188191194197200203206209212215218221224227230233236239. . .272275278281284287290293296299
The following [Table 3] presents a sequence for reading the data registered in the [Table 2] to interleave the data according to the tone interleaving scheme.
TABLE 30306090120150180210240270. . .63666961261561862162462769396999129159189219249279. . .154575105135165195225255285184878108138168198228258288. . .245484114144174204234264294275787117147177207237267297. . .43464941241541842142442747376797127157187217247277. . .134373103133163193223253283164676106136166196226256286. . .225282112142172202232262292255585115145175205235265295. . .23262921221521822122422725356595125155185215245275. . .114171101131161191221251281144474104134164194224254284. . .205080110140170200230260290235383113143173203233263293. . .295989119149179209239269299
As described above, interleaving is carried out to correct errors that have occurred during data transmission. However, with the symbol interleaving scheme or the tone interleaving scheme, the transmission errors of the data transmitted from the transmitting end cannot be completely corrected in the receiving end. Therefore, the transmitting end requires an interleaving scheme that can correct the transmission errors completely in the receiving end. Moreover, since the interleaving needs processes of recording data in the memory and reading the recorded data, data transmission delay occurs.